This invention relates to a method and apparatus for drilling a plurality of holes in sheet-like material, especially multi-ply printed circuit board material.
One feature of the invention provides a drill bit changing arrangement which maintains replacement bits in an array in a supply tray located above the drills so that no interference will be occasioned therebetween. The storage capacity of the supply tray of the invention is thus not limited by those considerations which would impose restriction upon a supply which is required to move to locations proximate the drill for a bit changing operation. This also allows supply tray replacement during the drilling operation. Other features of the invention comprise a flipper having pockets in which bits are receivable for lateral transfer to and from a central axis of each drill for the bit changing operation and a vacuum tube "picker" by which the bits are transferred back and forth between the flipper and the supply tray.
Accordingly, the invention provides a bit changing arrangement which alleviates problems of interference of the supply with the work piece or the drill, while enhancing the bit storage capacity and drilling machine versatility.
Of the prior art cross referenced above, U.S. Pat. No. 2,267,336 discloses interchangeable inserts 35 for a pressure foot 34, but there is no provision for or suggestion of a drill bit supply and/or changing means therein. Even more importantly, this reference does not disclose or suggest scrap evacuation and the problems inherent therein.
Each of the other cross referenced patents discloses an individual drill and laterally displaceable tool changer for the drill, with the replacement drill bits being stored in an adjacent endless conveyor or carousel or a supply integral with the housing of the drill.
Other features of the invention will become apparent from the following disclosure.
The invention is directed to a method and apparatus for selectively and simultaneously drilling a plurality of holes in thin panels such as printed circuit boards, while providing for automatic changing of the drill bits, individually or plurally, as required. A tray of drill bits is driveable in X and a row of vacuum pickers are driveable in Y, so that the various bit locations of the tray are addressable by such X-Y positioning, and selectable vacuum pickers are extensible and retractable so as to pick and place the drill bits at various matrix locations of the tray. The vacuum pickers also are extensible and retractable through corresponding tray openings in order to deliver replacement bits to, and retrieve used bits from, a flipper assembly associated with each drilling module. Each flipper assembly transfers bits back and forth between the vacuum picker and drill without having to transfer either bit through the opening in a footprint portion of the pressure foot which engages the materials to be drilled during the drilling operation. Thus, the footprint opening may be made smaller in diameter than depth stop collars or the like which are of greater diameter than the working portion of the bit which is advanced through the footprint opening during drilling. This smaller footprint opening of the pressure foot is for minimizing or eliminating hole "smears" and for overcoming problems normally associated with the so-called "oil can effect".
The replacement bits utilized in the industry for which the instant invention is particularly applicable generally have depth stop collars attached to the drill bits prior to their supply to the drill. These collars generally are adjustably positioned along the length of the drill bit so as to compensate for changes in the length of the bit, as might occur upon resharpening of a bit, and thus to maintain a preferred depth of penetration of the bit into the work. Since the drill bits utilized in this industry generally have been changed heretofore by passing them through the bottom hole of the pressure foot while the collar is still attached thereto, and since the collars are larger in diameter than the drill bits, a larger footprint opening is required in the pressure foot generally used with these drills.
Excessive burring and wicking path fractures can and do occur from the "oil can effect" on the material being drilled when the footprint opening of the pressure foot is relatively much larger than the diameter of the drill bit.
A further disadvantage of having such an enlarged hole in the bottom of the pressure foot is that the vacuum drawn on the pressure foot, in order to evacuate the scrap or chad circuit board material therefrom, is not concentrated upon the flutes of the drill bit as much as when the hole of the pressure foot is much closer to the size of the bit itself. Thus, the chad that is not removed from the flutes is transferred onto the internal surfaces of subsequently drilled holes, so that these bits of chad become packed at various spots along the internal diameters of the subsequently drilled holes.
Typically, the internal diameters of these holes have copper applied thereto during water and chemical "electroless" baths such that water can get in or behind the packings or so-called "smears" of chad. Ferrules of copper are then electroplated onto the initially applied copper, and the water behind the resin packings can cause "pops" in the final ferrules upon passing of the boards through subsequent reflow or wave soldering processes at which temperatures typically reach 550.degree. F. Even if the ferrule does not pop, it is weakened sufficiently to cause electrical failures during the subsequent expansion and contraction thereof in normal use. Further, the epoxy resin "packing" can serve as an insulator blocking a required electrical connection between internal copper tracks of multiple layer boards and the finished copper ferrule.
Thus, there is a definite need in the industry for eliminating such packings or smears of chad on the inside diameters of the drilled holes. Heretofore, in order to overcome this problem, the resin portions of the hole have been etched away to a larger diameter than the copper layer portions by means of sulfuric acid or plasma or the like.
By the instant invention, drill bits are changed without passing through the bottom hole of the pressure foot so that the hole may be much closer in diameter to the working portion of the drill bit. Thus, there is an increased vacuum effect in the footprint opening upon the chad caught in the flutes of the drill bit during retraction of the bit from the material. Still more concentration of the vacuum in the drill flutes may be provided by grooving or fluting the internal surface of the pressure foot in or near the inner surface of the footprint opening so as to cause a swirling air flow.
These and other features of the instant invention and their distinctions over the prior art will become more apparent from the following detailed disclosure. The invention comprises several steps and the relation of one or more of such steps with respect to each of the others and the apparatus embodying features of construction, combinations of elements, and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure.